The subject matter of this proposal is N-pinhole gamma-emission computed tomography, a generic name for the tomography of the seven-pinhole collimator and the time-coded aperture. Both of these tomographies involve computer reconstruction of the three-dimensional distribution of a radioisotope in the human body from the externally measured projection pattern of the emitted gamma-rays. The above tomographies assume radioisotopes which emit a single gamma of interest per decay. These radioisotopes are currently better established in the majority of nuclear medicine clinics than are those which emit positrons. To date, the chief clinical utility of N-pinhole tomography has been in heart studies, both gated and ungated, and thyroid studies. The objectives of this research are to: 1. Optimize present N-pinhole tomography. This optimization will be done by carrying out three-dimensional simulations of the data acquisition, then varying the algorithms to produce the best reconstructions and, finally, varying experimental techniques to make the results with real data match those of the simulations. 2. Through the use of three-dimensional simulation, compare seven-pinhole tomography to coded-aperture tomography for the same pinhole size and the same range of angular sampling. 3. For simulated and experimental coded-aperture data, compare the reconstructions from the Algebraic Reconstruction Technique and the seven-pinhole algorithm. 4. Characterize the results of N-pinhole tomography qualitatively and quantitatively. 5. Develop a fast method for predicting the image by convolution. Check the prerequisite for the above that linear and non-linear algorithms give the same result for volume objects. 6. Investigate new data-acquisition situations designed to improve N-pinhole-tomography's relatively poor depth resolution.